在不同的servlet之间共享资源

Question

Let's say I have a certain resource S (for instance a strange database that uses the filesystem) and I have a certain Java class R that manage that resource (it prvides high level api and manages stuff like concurrency necessary in the use of S). Now I have the constraint that if an instance of R manages S then no other instance of R can access to S at the same time.

Now, let's assume I have a servlet V1 that needs to access S through R. I want to allow many users to work with V1 concurrently, so since the container will assign a new thread of V1 to each user, I thought to make R static, initilize it in the init() method so as to share it among the threads. Is this ok?

case two: Now I have M different servlets V1,...,VM each accessible from many users. Now I want that all these servlets can have a rw access to S. I must access S through R and I can't simply use an instance of R for each servlet because only one instance at time can deal with S. Is there any way to share R among all the threads of all the servlets?

ps. R in my case is an embedded database like neo4j.

Answer 1

You can have a static initializer on R to create the one and only instance of R and store it in some static field (accessible via a static getter).

You could also create and initialize one instance of R by implementing a ServletContextListener . The contextInitialized method is called when the web app starts.